This invention relates to blasting signal transmission line and in particular to blasting signal transmission line utilizing a hollow flexible tube and a combustible substance in the interior of the tube for transmitting a blasting initiation signal along the length of the tube.
In mining and other operations requiring blasting of rock or minerals or the like there is generally required a predetermined time between detonation of individual blasting charges. To detonate a plurality of these individual blasting charges, transmission lines are employed from a central initiating point to send a signal to initiate the detonation of the individual charges. Normally, these signal transmission lines consist of one or more main trunk lines connected to a plurality of down lines.
The availability of signal transmission line with only limited, fixed signal velocities has led to the use of separate delay units to control the time transmission of a blasting initiation signal. For example, detonating cord generally transmits an initiation signal at a rate between about 4,000 and 9,000 m/sec. (13,100 and 29,500 ft/sec.) To avoid the use of separate delay units, such detonating cord propagation rates would require the use of cord lengths in the range of 32 to 72 m (105 to 240 ft.) between charges to achieve the convention minimum required time delay interval of 8 milliseconds. in U.S. Pat. No. 4,402,270 to McCaffray there is disclosed a high detonation velocity detonating cord having a signal velocity of at least 6,500 m/sec. (21,000 ft./sec.) which may be modified by inserting elongated flexible blockage elements which completely block the hollow core of the cord at selected locations along the length of the cord. The detonating cord of this type not only has a very high signal velocity but also self destructs upon use.
Non destructing blasting signal transmission tubes have also been utilized to carry a detonating signal. These signal transmission tubes generally carry a signal at a considerably lower velocity than that of detonating cord so that a shorter tube length may be utilized to control the timing between charge detonation. As used herein, the term "signal transmission tube" refers to any detonating or deflagrating transmission line with, in the preferred embodiment, a flexible hollow tube and a self-oxidizing combustible substance disposed within or along the interior of the tube for carrying a detonating or deflagrating signal.
Such signal transmission tube may be any of the different available types, for example, shock tube having a detonating powder coated on the inner periphery of the tube as disclosed in U.S. Pat. No. 3,590,739 to Persson. Shock tube generally carries a pressure pulse signal at approximately 2,000 m/sec. (6,500 ft./sec.) Also available is transmission tube containing a loosely filling combustible substance inside the tube as disclosed in U.S. Pat. No. 4,290,366 to Janoski.
A signal transmission tube having a lower signal velocity than shock tube is disclosed in copending U.S. patent application Ser. No. 811,731 which discloses a transmission tube having a deflagrating substance on the inside of the tube to transmit a blasting initiation signal in a flame front at velocities up to about 1,500 m/sec. (4,900 ft./sec.).
While signal transmission tube can then be obtained in a variety of signal velocity capabilities, the specific velocity selected in each of these tubes is a function of the specific combustible substance used therein and the surface area of that substance available for combustion. Thus, the signal velocity of each of these tubes is essentially fixed upon production of the tube and cannot be modified thereafter. In addition, the sensitivity of the combustible mixture within each tube is generally related to the velocity of signal propagation so that the higher sensitivity mixtures are also the highest velocity mixtures. Consequently, in those systems where signal initiation sensitivity is important, the user is left with little option but to use the highest velocity signal transmission tubes.
Bearing in mind these and other deficiencies of the prior art, it is therefore a primary object of the present invention to provide signal transmission tube with improved control of blasting signal velocity.
It is another object of the present invention to provide signal transmission tube which has a controlled signal velocity substantially independent of the combustible substance contained therein.
It is a further object of the present invention to provide signal transmission tube for which signal velocity may be modified after production.
It is yet another object of the present invention to provide mechanical techniques for modifying signal velocity in signal transmission tube.
It is a further object of the present invention to provide a process for producing such improved signal transmission tube.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.
A better understanding of the objects, advantages, features, properties and relations of the invention will be obtained from the following detailed description and accompanying drawings which set forth certain illustrative embodiments and are indicative of the various ways in which the principles of the invention are employed.